1. Field of the Invention
This invention relates to a dry type developing device for use in an image formation apparatus using the electrophotographic method or the like.
2. Description of the Prior Art
FIG. 1 of the accompanying drawings schematically shows a dry type developing device according to the prior art. A hopper-shaped container 6 for storing developer therein has an upper lid 11 which can be opened and closed so that fresh developer may be supplied thereinto whenever required. In the lower opening of the container 6, there is provided a developing roller 2 having a magnet roller 4 disposed in a cylindrical nonmagnetic developer supporting member 3 (hereinafter referred to as a sleeve). The sleeve 3 and the magnet roller 4 can be driven independently of each other and therefore, if the magnet roller 4 is fixed and the sleeve 3 is rotated in counter-clockwise direction C.sub.2 or both are rotated but the speed of rotation of the sleeve in the direction C.sub.2 is somewhat higher than the speed of rotation of the magnet roller 4 in clockwise direction C.sub.1, then the developer sticking to the sleeve 3 can be conveyed toward a latent image bearing member. The developer, when conveyed out of the container 6, is formed into a thin layer by a blade 5 secured to the container 6. As a result, in the developing station D, the developer on the sleeve 3 adheres to the latent image bearing member 1 in accordance with the charge possessed by the latent image thereon, whereby the latent image is developed and visualized in accordance with each color tone.
However, in the above-described dry type developing device according to the prior art, when foreign substances enter into the developing device, the surface of the sleeve 3 may be scratched or locally abraded by the foreign substances, so that a uniformly thin layer of developer cannot be held on the sleeve 3 or the life of the sleeve 3 is remarkably shortened, thus making it difficult to obtain images of good quality.
In some cases, a uniform rough surface is provided on the sleeve by machining in order to improve the developer conveying characteristic of the sleeve. The assignee of the present invention has previously proposed a method of forming a rough surface on the sleeve in copending U.S. application Ser. No. 138,909. However, as the wear of such rough surface progresses, the conveying characteristic of the sleeve is reduced. As a result, the developer conveyed from the container 6 onto the sleeve, as shown in FIG. 2 on the accompanying drawings, creates lumps B due to the developer A swelling out from the tip end of the blade 5, and this has led to the disadvantage that irregularity of development or the like is caused.